Since there will be no shoot-out at high noon over the GOP presidential nomination, the convention that opens officially Monday may seem more like a made-for-TV Busby Berkley musical, with a predictable plot line and the necessary "serious stuff" pancaked in sex appeal, fancy footwork and a lot of close harmony.

To set the theme of the convention -- "Together . . . A New Beginning" -- Ronald Regan's California cowboys have decided to punch up the opening night with an hour of music and patriotic soliloquies by such prominent Republicans as Donny and Marie Osmond, Michael Landon, Wayne Newton, Jimmy Stewart, Vikki Carr, Vicki Lawrence, Ginger Rogers, Susan Anton, Buddy Ebsen, Dorothy Hamill, Chad Everett, Efrem Zimbalist Jr. and Lyle Waggoner.

Of course, there also will be lots of regulation politicians in the spotlight this week at Joe Louis Arena. From Henry Kissinger to Barry Goldwater, as one GOP official phrased it, "the full spectrum of Republican thought."

But this is a convention whose managers have said is, to an unprecedented degree, designed for television.

And the four-day program is heavily smudged with the grease-paint fingerprints of the man destined to be the GOP nominee, who before he became governor of California spent most of his life playing romantic leads, and of California's lieutenant governor, Mike Curb, a millionaire former record producer, Reagan aide and convention program chairman.

The convention's traditional keynote address, to be delivered by Michigan Rep. Guy Vander Jagt, has for the first time been pushed back to the second night to make room for a birthday party honoring former president Gerald Ford, followed by the entertainment hour.

Indeed, using the electronic Cuisnart of pop culture, the philosophy of this particular convention threatens to obliterate the murky boundaries between show biz and politics once and for all.

As Curb put it in as earnest explanation "Michael Landon and Susan Anton were invited to appear because they are an actor and actress. They were picked becuase of their high approval rating among the 18-to-34-years-olds."

Curb acknowledged that there is a danger of reinforcing Reagan's "Bedtime for Bonzo" image as a Grade B Hollywood lightweight. "I spent two hours with [Reagan] and Nancy going over just that problem. The last thing we want to do is have this look like a Hollywood spectacular . . . .

"It's simply a group of prominent Americans talking about their belief in the party, or the nation . . . their ideas."

The celebrities were carefully selected, he said, on the grounds that they each "represent the views of a substantial constituency" of Americans.

"Donny and Marie Osmond are from Utah; they are certainly not what you'd call Hollywood entertainers . . . they have a good youth following, especially a middle-American youth following."

As for champion stock car driver Richard Petty, Curb went on, "he represents a major constituency. That NASCAR constituency is huge throughout the Carolinas, Florida, Alabama and so forth.

"Jimmy Stewart -- heS looked upon more as a great American than an "actor."

Vikki Carr -- "I wouldn't call her Hollywood but a leading representative of the Mexican American community."

There will also be the Whitney Family, a black rock group from Los Angeles, and, for good measure, 2,000 young people from the Detroit school system, including, Curb said, "a substantial minority representation."

The first-night appearance by Ford, Regans' former political rival, is designed to set a tone of unity, Curb said.The former president, a native sone of the convention's host state who has since joined the California set by moving to Palm Springs, will celebrate his 67th birthday with a cake, candles and a speech.

The first night, in fact, has been designed for what convention program director Ken Reitz calls "marquee value." The theory, based on research of past conventions, is that the larger the opening night audience, the more who will watch on subsequent nights. (Traditionally, the pattern has been for highest ratings on the first night, a drop-off on the second and third and a recovery on the final night.)

The only drama of the "together" convention is expected to come Thursday, when Reagan selects a running mate out of the chorus line.

Meanwhile, the contenders for that honor will compete for rave reviews in a series of addresses that pepper the schedule: Indiana Sen. Richard Lugar in the relative obscurity of Monday afternoon; former treasury secretary William Simon and former defense secretary Donald Rumsfeld Monday evening; New York Rep. Jack Kemp Tuesday evening, George Bush on Wednesday evening, and Tennessee Sen. Howard H. Baker Jr. on Thursday night.

Goldwater and Kissinger will speak on Tuesday evening, with unsuccessful presidential candidate John Connally in between.

To accommodate the rhythm of television and viewer attention spans, the planners said they are determined to keep the convention events snappy.

It was this same team, Curb and Rietz, a California political television expert, who engineered much of Richard Nixon's 1972 renomination convention in Miami, where the program was so tight that 10 seconds were allowed at one point for "spontaneous" applause.

For this year's gathering, the two have trimmed the number of convention hours from 30 (as in 1976) to 18, and they say they hope to end each night on time at 11 p.m. (EDT).

Ford and other Republicans of a certain stature will be allowed to speak as long as they want, the managers indicated. But they are encouraging most speakers to hold it down to eight to 10 minutes or even less.

And for major addresses, at least, in order to encourage TV cameras to focus on the podium, they plan to spotlight the stage but drop the lights on the audience of potentially distracting or distracted delegates.

What viewers see on their television screens will not necessarily be what is happening in the spotlight, of course.

Network officials maintain they will not be led around by the nose by convention managers, although in some cases their alternatives look rather sparse.

"It's their convention, so they can do whatever they wish," said Ernest Leiser, vice president of special events for CBS. "But it does seem to us this [entertainment hour] isn't what a convention is for. I guess it shows there's a death of real political events to be covered here . . . ."

The networks have prepared alternative material to be run in place of the official proceedings as they see fit as always, officials said.

The lack of high drama notiwithstanding, the convention managers are aware that past televised conventions have given candidates an immediate boost in popularity polls. President Carter jumped more than 10 percentage points in one poll immediately after the harmonious and suspenseless 1976 Democratic National Convention.

Reitz said he anticipated there would be criticism of his and Curb's unconventional approach. "There always is when anything is done for the first time. What's important is the impact of what we do, both on the viewers and in the hall."

As showman George M. Cohan observed, "Many a bum show has been saved by the flag." Republican convention managers, always hip to that philosophy, are adding more stars to their stripes.